DECONSTRUCTING TONGANOXICHNUS: MORPHOLOGY, BEHAVIOR AND A NEW ICHNOSPECIES FROM MASSACHUSETTS

The ichnogenus Tonganoxichnus Mángano, Buatois, Maples and Lanier 1997, can be described as a discrete, bilaterally symmetrical impression (negative epirelief or positive hyporelief) with a main medial imprint, a pair of anterior oblong imprints and a posterior elongate medial imprint. Based on favorable comparisons with the body plan and behavior of archaeognathan insects, the ichnogenus has been interpreted as the full body impression of such insects. As more specimens of Tonganoxichnus exhibiting a wider range of morphologies and behaviors are discovered, it is possible to make new interpretations regarding the identity and behavior of these primitive insects. Three ichnospecies currently exist within the ichnogenus and represent various behaviors and body morphologies. A new ichnospecies, T. attleboroensis, is proposed based on material from the Pennsylvanian Wamsutta Formation of Massachusetts, the fourth from North America. A new ichnotaxobase for the group, details of the abdominal imprint and abdominal appendage locations, is key to the differentiation of the new species. T. attleboroensis shows uniramous abdominal appendage impressions that articulate in a lateral position as opposed to the medial position in T. buildexensis. These appendages are also relatively short and commonly, but not necessarily, have a divergent orientation with respect to the plane of symmetry. The differences in relative location, orientation and size of abdominal appendage impressions among Tonganoxichnus ichnospecies may relate to real morphological differences among archaeognathan tracemakers and/or behaviors that have not yet been considered. These potential alternative behaviors and body plans have direct bearing on the mode of trace preservation and the paleoenvironmental interpretation of the rocks in which they are found.